Insulating material



Feb. 22, 1949. E, SCHULMAN ETAL f 2,462,228

INSULATING MATERIAL Filed May 24, 1944 Bonding rlgem' bmprz'sz'n; [xi/acted Pine Wood Pita/2 and 005101 Oil. 7

INVENTORS Earl L. Schulmarz Patented Feb. 22, 1949 INSULATING MATERIAL Earl L. Schulman and Robert D. Jerabek, Wilkinsburg, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh-Pm, a corporation of Pennsylvania Application May 24, 1944, Serial No. 531,032

This invention relates to insulating compositions, and more particularly to flexible laminated insulating compositions suitable for use in elec- "trical apparatus.

In the construction of electrical apparatus large amounts of laminated electrically insulating material of all kinds are required. In certain applications the electrically insulating material is applied by winding or shaping to some predetermined form in order to accommodate coils or other electrical conductors. In order to achieve flexibility it is common to employ laminated insulating materials bonded with a binder containing a portion of an evaporable solvent to soften the binder. Employing this latter type .of material, the prepared flexible laminated insulating material must be carefully stored, asin airtight containers, and handled .binder, the binder resisting hardening on drying and ageing. I

A further object of the invention is to provide a permanently flexible binder for preparing composite electrical insulation, the binder having good electrical properties and being insoluble in petroleum oils.

For a fuller description, reference should be had to the following detailed description and drawing wherein:

Fig. 1 is a perspective view of a laminated Fig. 2 is a greatly enlarged, fragmentary crosssection view; and

Fig. 3 is a perspective view, partly in section of a tape.

According to the present invention a flexible binder capable of uniting mica flakes into composite insulation is prepared by combining extracted pine wood'pitch with castor oil. The

combination of ingredients when mixed together has good adhesion for mica flakes while permit- 2 Claims. (Cl. 154-23) U ting flexing and binding of the laminated product.

The extracted pine wood pitch employed in the present invention is a complex resinous material whose exact composition is not known but comprises the residue remaining 'after the separation of rosin, turpentine, pine oil and other products from the mixture produced by a practically complete extraction of pine wood with a solvent. In the process of producing the residue, pine wood in the form of chips is subjected to the action of a powerful solvent, such as benzol, with or without the application of steam to increase the amount of extract obtained. The solvent is then removed from the resinous matter so extracted from the pine wood chips and the solute is fractionated by subjecting it to the action of specific solvents and heat to separate turpentine, rosin, Dine oil .and other constituents. The final residue is a hard brittle complex organic substance which is hereafter described as extracted pine wood pitch. Such a material is produced and sold at the present time under the trade name Vinsol.

The extracted pine wood pitch by itself is so brittle and relatively non-adherent to mica that its use as a binder in making laminated mica products is unsatisfactory. We have found that when combined with castor oil in the proportions of about 100 parts'of extracted pine wood pitch to from about 60 to 100 parts by weight of castor oil, that the combination possesses highly satisfactory properties as a binder for mica flakes.

In preparing the composition, a satisfactory process comprises dissolving the extracted pine wood pitch in a large volume of a solvent therefor. It has been found among many suitable organic liquids, that ethyl alcohol, methyl al- 1 cohol and acetone may be used for this purpose.

Denatured alcohol will generally be preferred, both on account of its low cost as well as its low order of toxicity. Thereafter, the castor oil is added. to the solution of the extracted pine wood pitch in the solvent.

A small amount of pine tar may be added, for example, up to 5 parts by weight per parts of extracted pine wood pitch.

In preparing the solution ofthe binder, the requirements for a satisfactory solution for application. to mica flakes .had been found to be somewhat critical. The best manufacturing results have been obtained when the solids content of-the solution has been maintained within the limits of from 34% to 36% solids. The solids content may be varied considerably from this emes I proportion, but the percentage of binder deposited on the mica flakes and other factors change accordingly.

The following examples of various compositions according to the present invention have been found to be highly successful in practice:

was prepared by dissolving the first three ingredients in the ethyl alcohol in the order given. The solution so prepared was employed in the conventional mica plate building machines in the same manner that shellac solutions are applied.

A flexible mica sheet, such as shown in Figs. 1 and 2 of the drawing. was produced after evaporating the solvent and pressing at a temperature of say 125 C. The plate In is composed of a plurality of mica flakes I! with the extracted pine wood pitch and castor oil binder ll applied thereto.

The electrical properties of the mica sheet l are as follows:

The binder in sheet I0 is insoluble in transformer oil and other petroleum products. The sheet remained flexible for nearly a year when exposed to the air without any indication of increase in stiffness. The sheet is quite flexible and may be bent without fracturing or rupturing about relatively sharp radii considering its thickness.

Exaurnr: 2

A composition suitable for making mica tapes and wrappers of various kinds was composed as follows:

Extracted pine wood pitch pounds 382 Castor 011 do 270 Ethyl alcohol gal1ons 177 The solution was applied to mica flakes laid upon a fabric. The fabric and mica flakes were well bonded upon evaporating the solvent and pressing the combined materials while warm.

As shown in Fig. 3 of the drawing, the tape l8 consists oi the sheet fibrous material having applied thereto mica flakes l2. The sheet fibrous material 20 may consist of cambric, glass cloth, flsh paper, Jap paper, cement paper, asbestos paper, asbestos cloth and other flbrous materials known to those in the art. Excellent adhesion has been obtained between these sheet flbrous materials and the mica flakes when the binder of of time.

the present invention is applied thereto. Not only the backing of the tape but the face likewise may consist of the same, or a different sheet material. In making slot insulation, for instance. one face or the mica flake body may carr glass flber cloth to form theinterior surface to come in contact with the conductors or winding, and the other face may consist of a smooth, tough paper, such as flsh paper. to permit easy insertion within the slots in magnetic cores.

The properties of the composition of Example 2 comprise a high degree of flexibility even when exposed to the atmosphere for prolonged periods The tape II, for example, may be wrapped about flne conductors or coils with good conformation characterized by lack oi! wrinkles and bulging. The electrical properties are similar to those given for the composition of Example 1.

Bxmu 3 A composition or intermediate flexibility comprised the followlng ingredients:

Extracted pine pitch pounds 335 Castor oil do 228 Pine tar do 9 Ethyl alcohol .gallons- 177 free, resides in the lack of adhesion to kraft paper.

After a mica sheet, for example, has been heated in an oven to evaporate most of the solvent therefrom, the warm sheet is placed in a press having a sheet of kraft paper between the platens and the mica sheet. After pressing at pressures of 100 pounds per square inch and higher, the mica sheet may be separated from the kraft paper liner without any difllculty. This characteristic has value since it facilitates manufacturing of the mica sheets.

It will be appreciated that the flbrous sheet material, such as glass cloth and the like, may be pretreated with other resinous materials in order to impart thereto other predetermined requirements, such as increased tear resistance. Thereafter the treated fibrous sheet material may be employed as a base to be combined with the mica flakes and the binder of this invention into a suitable insulating material.

Since certain changes in carrying out the above processes and certain modifications in the articles which embody the invention may be made without departing from its scope, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. A flexible electrically insulating material comprising mica flakes and a binder therefor composed essentially of 100 parts by weight of extracted pine wood pitch obtained by flrst extracting pine wood with a coal tar solvent and,

second, removing the volatile constituents from said extract and, third, extracting from the residual resin petroleum hydrocarbon soluble components, and from about to parts by weight of castor oil.

2. Insulating material comprising, in combination, aflbrous sheet, mica flakes applied to the fibrous sheet, and a flexible bonding agent composed of 100 parts by weight of extracted pine wood pitch obtained by flrst extracting pine wood 5 6 wlth a coal tar solvent and, second, removlnz the UNITED TENT volatile constituents from said extract and, third, STATES PA extracting from the residual resin petroleum 118- Number Name Date drocarbon soluble components, and from about 985,399 Cooper Feb. 28, 1911 60 to 100 parts by weight of oastor 011 to bind the 5 2,060,856 DeBell Nov. 17, 1936 sheet and the mica. flakes into a. whole. 2,114,392 Lane Apr. 19, 1938 2,199,224 Hughes Aug. '30, 1940 E h SCH 2,291,961 119.11 1 Aug. 4, 1942 ROBERT D. JERABEK. 2,359,972 DeBell Oct. 10, 194.4

OTHER REFERENCES REFERENCES CITED The following references are of record in the xga g fi Hercules Powder page spubt file of this patent: 

